Manufacturing processes of semiconductor devices or liquid crystal panels include liquid processing processes, such as cleaning or etching. Liquid processing processes include applying processing liquid to target objects or dipping target objects into processing liquid. Processing liquid can be produced by mixing stock solutions in a predetermined ratio. Various processing liquid can be used in liquid processing processes. Processing liquid for used in a cleaning process, for example, is shown in Table 1 below.
TABLE 1NameMixing RatioUseMixture of Ammonia Water andNH4OH:H2O2:H2O =Remove ParticlesHydrogen Peroxide Solution1:1:5 (Volume Ratio)Remove Organic AcidMixture of Hydrochloric AcidHCl:H2O2:H2O =Remove Metallic Pollutantsand Hydrogen Peroxide Solution1:1:5 (Volume Ratio)Mixture of Sulfuric Acid andH2SO4:H2O2 =Remove Organic PollutantsHydrogen Peroxide Solution4:1 (Volume Ratio)Remove Metallic PollutantsHydrofluoric AcidHF (about 0.5-10%)Remove Si (Natural) Oxide LayerRemove Metallic Pollutants(Remove Cu)Buffered Hydrofluoric AcidHF:NH4F = 7:1Remove Si (Natural) Oxide LayerSolution
Plants may require dedicated pipes for each processing liquid when producing various processing liquid and supplying the produced processing liquid to each substrate processing apparatus. As a result, a plant will have a complicated inner structure, which will not be practical. Accordingly, plants include pipes to supply stock solutions for producing processing liquid to each substrate processing apparatus. Also, each substrate processing apparatus includes processing liquid mixing apparatuses to produce processing liquid.
Some processing liquid mixing apparatuses have been suggested in order to have constant mixing ratio of stock solutions in processing liquid. For example, Japanese patent unexamined publication no. 2003-275569 discloses a processing liquid mixing apparatus, including mixing tanks to mix various stock solutions, a flow controller to control an amount of the stock solutions, and a supply time controller to control supply time of each stock solution to the mixing tanks so that each stock solution can be supplied to the mixing tanks at the same time.
However, the processing liquid mixing apparatus disclosed in the Japanese patent unexamined publication no. 2003-275569 cannot control a supply rate of each stock solution to the mixing tanks, while it can control a total amount (that is, an accumulated flow rate) of each stock solution supplied to the mixing tanks and the supply time of each stock solution to the mixing tanks.
Generally, the flow controller gradually increases the flow rates of stock solutions supplied to the mixing tanks after the discharge of the stock solutions starts, and maintains the discharge rates of the stock solutions constant if the flow rates of the stock solutions reach a predetermined value. The time for increasing the flow rates of the stock solutions to the predetermined value after the discharge of the stock solutions starts is in proportion to set flow rates.
Accordingly, the processing liquid mixing apparatus disclosed in the Japanese patent unexamined publication no. 2003-275569 cannot make the flow rate proportions of stock solutions supplied to the mixing tanks to be coincided with the mixing ratio of the processing liquid at certain supply time. In particular, at an initial supply time, the stock solution having a relatively high set flow rate cannot reach the set flow rate while the stock solution having a relatively low set flow rate can reach the set flow rate. Thus, an amount of the stock solution having the relatively low set flow rate becomes greater.